Computer motherboards typically include a number of slots into which expansion cards may be installed to supplement the functionality that is integrated onto the motherboard itself. For example, a graphics card might be installed in one expansion slot, a network interface card in another expansion slot, and so on. Motherboards also typically are designed to comply with one or more industry standard form factors so that they may be used with enclosures and power supplies from a variety of manufacturers.
One of the challenges that face designers and manufacturers of motherboards is that expansion card interface technology continually changes. For instance, at one time the most popular expansion card interface technology was ISA technology. Later, PCI technology began to replace ISA technology. Then AGP technology was introduced for accelerated graphics, and PCI technology evolved to include PCI-Express variants. Moreover, transitions from one expansion card technology to another do not occur at discrete times; rather, they occur over periods of years. Therefore, motherboard manufacturers generally must support more than one type of expansion card interface technology simultaneously on a single motherboard.
In recognition of this challenge, the popular industry-standard ATX form factor allows for up to seven expansion slots on a single motherboard, and these seven slots may be occupied by a variety of different technologies. For example, three of the slots might be configured to receive ISA expansion cards, two of the slots might be configured to receive PCI expansion cards, one of them might be configured to receive either an ISA or a PCI expansion card, and the seventh slot might be configured to receive an AGP graphics expansion card.
While the ATX form factor thus provides some flexibility for motherboard manufacturers in this regard, it also imposes significant constraints: The ATX form factor contemplates no more than seven expansion slots on a single board, and those seven slots must be placed in very specific locations measured relative to prescribed motherboard mounting holes and relative to the edges of the motherboard itself. It would be desirable to provide more than seven expansion slots on a single motherboard to support a greater variety of expansion card technologies, and to do so in a manner that allows the motherboard to remain compliant with industry standard form factors such as the ATX form factor.